A single, distinct sellable item: one product in one variant (size, colour, configuration). SKU count is a discipline, not a vanity metric, every extra SKU adds inventory risk, forecasting complexity, and cash tied up in stock. The strongest DTC brands usually win with a tight range and a clear hero, not a sprawling catalogue.
Benchmark. Watch the share of revenue from your top SKUs. If a long tail of SKUs each contributes little, it is usually costing more in complexity than it earns.